The present invention relates to a record player of the direct drive system, and more particularly to the prevention of vibrations during the rotation of a turntable.
FIGS. 1 and 2 are a front view and a plan view showing an example of a prior-art record player of the direct drive system. Referring to the figures, numeral 1 designates a cabinet, and numeral 3 a driving motor which drives a turntable 2 to rotate. Numeral 4 indicates a tone arm which holds a cartridge at its fore end, and numeral 6 insulators which resiliently hold the cabinet 1.
Here, in driving the turntable 2 by means of the driving motor 3, a torque (indicated by arrow R in FIG. 2) acts. On the other hand, as a counteraction against the torque, a torque in the opposite direction (indicated by arrow L in FIG. 2) acts on the cabinet 1 on which the stator of the driving motor 3 is mounted. In such case, forces based on the action and the counteraction become equal in magnitude and opposite in direction. In a case where the driving motor 3 rotates in a constant-speed state and where the developed torques undergo no change with time, a stress ascribable to the counteraction on the cabinet 1 remains at a constant value. In actuality, however, even when the driving motor 3 is in the constant-speed drive state, the developed torques change every moment and also the counteractive force on the cabinet 1 changes vibratorily every moment. In this regard, in a case where the insulators preventive of floor vibrations are not disposed and where the cabinet 1 is placed directly on an object of sufficiently great mass, the rotational vibrations of the cabinet 1 are very small. In order to reduce the influence of the floor vibrations, however, the cabinet 1 needs to be held through the insulators 6 made of an elastic material. In case of employing such insulators 6, the cabinet 1 induces the rotational vibrations on account of the vibratory counteraction ascribable to the torque fluctuations. These rotational vibrations vibrate, not only the cabinet 1, but also the tone arm 4 carried thereon. Accordingly, they affect the playback signal of a record very adversely. In particular, they form causes for the cross modulation distortion and deterioration in the S/N (signal-to-noise) ratio and also deteriorate the phase distortion characteristic etc.
As thus far described, in the record player of the so-called direct drive system wherein the turntable is directly driven by the motor, the cabinet as well as the tone arm is inevitably affected adversely by the counteraction due to the torque based on the rotation of the motor.